The present invention relates generally to the field of optical systems, and more particularly to a uniquely configured wide field of view heterodyne receiver specifically adapted to efficiently mix a received signal defining a first wave front and a local oscillator signal defining a second wave front with the first wave front and the second wave front each being planar and parallel relative to each other.
Optical heterodyne detection of a modulated input signal occurs through mixing the input signal with a stable, fixed frequency signal (often called a local oscillator) in a nonlinear device such as a tube, transistor, or diode mixer to create an output signal. The combination of the two signals may then produce an output signal that is either equal to either the sum or the difference of the two input frequencies. The output signal may then be filtered, rectified, and/or amplified. The output signal may also be analyzed to determine the frequency, amplitude, or phase of the input signal and thereby yield an image or other useful information based on the input signal. This process may allow the detection of otherwise undetectable high frequency signals, and has a tremendous variety of uses, such as applications in military (thermal imaging, target tracking, surveillance, communications, etc.), atmospheric analysis, and astronomy, just to name a few.
Heterodyne detection may be done passively or actively. In passive detection, the input signal consists of the background radiation derived from a target. The background radiation would then be heterodyned with a local oscillator signal to create the heterodyned signal. In active detection, a reference signal, such as a laser, may be directed toward and reflected off of the target. The signal that is reflected from the target will be modulated by the target. The reflected signal may then be heterodyned with a local oscillator to create the heterodyned signal. In both passive and active detection, properties of the target may be determined via analysis of the heterodyned signal.
One of the objectives of an optical system utilizing heterodyne detection is to increase the signal-to-noise-ratio of the system, which is the ratio of the magnitude of the signal to the magnitude of the noise present in the system. As unwanted radiation is filtered from the system, a theoretical best noise may be achieved through heterodyne detection. In this regard, heterodyne systems may become very sensitive and much more effective because unwanted noise may be reduced or eliminated.
Currently, heterodyne detection has two significant limitations. First, efficient heterodyne detection has typically only been possible for point sources. For example, a given system may allow detection of a single field point in order to determine properties of that point, such as for three dimensional shape measurements. Thus, present systems only accomplish heterodyne detection for single point sources, and not over a large field of view. A second weakness of current heterodyne systems is due to resultant astigmatisms, interference fringes, aberrations and/or other optical flaws that reduce the effectiveness of the system. Such optical flaws are result due to system design and configuration. In these respects, heterodyne detection has heretofore been limited in its utility.
Heterodyne detection has been significant for enhancing optical research and detection of low-level point sources of radiation. Additionally, optical detection may also be enhanced utilizing other technologies. Specifically, contemporary optical systems use a dewar to further enhance the efficiency and effectiveness of signal detection. The dewar tends to block background noise from reaching a detector. The dewar typically utilizes cryogenics to cool components of the system, such as a cold stop, the detector, and a cold filter, all of which are located behind an optical window in a vacuum-sealed environment. The cryogenic environment of the dewar aids in eliminating the thermal component of noise in a received signal. Currently, dewar technology is not apparently utilized in conjunction with heterodyne detection.
Therefore there is a need in the art for a heterodyne detection system that provides detection over a wide field of view. There is a need in the art for a heterodyne detection system that enhances mixing efficiency over a wide field of view. Additionally, there is a need in the art for a wide field of view heterodyne detection system that mitigates against optical flaws through an enhanced alignment and configuration. Finally, there is a need in the art for a wide field of view heterodyne receiver that tends to provide a high signal-to-noise ratio.